Spark gap unit



Sept. 29, 1959 R. F. HUBER 2,906,922

SPARK GAP UNIT Filed May 28, 1958 INVENTOR.

RoNALD F. HuaER United States Patent O SPARK GAP UNIT Ronald F. Huber, Evanston, Ill., assignor to Joslyn Mfg. and Supply Co., Chicago, Ill., a corporation vof Illinois Application May 28, 1958, Serial No. 738,334

8 Claims. (Cl. 315-59) The present nvention relates to a spark gap unit and, rnore particularly, to a spark gap electrode arrangement employing structure for producing between the spark gap electrodes a magnetic field which eauses an are de- `;'eloped between the electrodes to move relative to the electrode surfaees. Specifically, the present nvention is an improvement over the spark gap unit disclosed in the copending application, Serial No. 507,284 of Edward H. Yonkers et al., assigned to the same assignee as the present nvention.

In the lightning arrester art, spark gap units including a pair of spaced apart electrodes are eonventionally used in lightning arresters to protect electrical equipment of various types from surge eurrents intercepted by the arresters. When the voltage of the surge reaches the sparkover voltage of the spark gap unit, a high current are is developed across the electrodes in order to produce a low impedance path for the surge current to ground. In order to achieve successful operation of the lightning arrester, it is imperative that the sparkover voltage of the spark gap unit remain substantially constant so that the unit will function properly for all voltages exceeding the rated sparkover and will not short out or bypass voltages below the sparkover value. In button-type electrodes frequently employed in lightning arresters, the high current are often pits and scars the electrode surfaees. The resultant surface irregularities cause field concentration and abnormal gradients for a given applied voltage. For this reason the pitted electrodes may not withstand its RF voltage required for the normal operation of the gap. In the unequally spaced electrode arrangement disclosed in the aboveidentified Yonkers et al. application, the are is initiated across the minimum are gap distance and then moves toward the ends of the electrodes as the are tends to lengthen. However, in this arrangernent, no provision is made for changing the location of the initial Sparkover points on the electrodes, with the result that after repeated sparkover of the gap, the su'rfaces defining the minimum are gap distance become pitted and scarred and, hence, the unit incurs the attendant disadvantages deseribed above with respect to changes in the sparkover voltage. Aecordingly, it would be desirable to provide a spark gap unit wherein the high current are is initiated at random locations on the electrode surfaces and immediately thereafter the are is continuously moved across the electrode surfaces to reduce the amount of electrode pitting and surface distortion.

Therefore, it is a prineipal object of the present invention to provide a lightning arrester including a spark gap unit which does not have the above deseribed disadvantages of the prior art devices.

Another object of the present nvention is to provide a spark gap unit wherein a magnetic field is producecl between spaced apart spark gap electrodes to cause an are developed thereaeross to move relative to the electrode surfaces.

It is a further object of the present nvention to proice vide in a spark gap unit an electrode which supports' structure for developing a magnetic field between the spark gap electrodes of the unit in order to move an are' established between the electrodes.

It is still another object of the present nvention to provide a spark gap unit embodying coplanar and concentn'c inner and outer electrodes, one of which supports ructure for producing a magnetic field having fiux lines perpendicular to the plane of the electrodes for moving an are around the inner electrode.

It is a still further object of the present nvention to provide in a spark gap unit eoneentric and coplanar inner and outer electrodes and an annular permanent niagnet eoncentrically related to and supported within one of the electrodes for establishing a magnetic field between the electrodes.

The above and other objects are realizecl, in accordanee with the present nvention, by providing a new and improved spark gap unit for use in lightning arresters. Briefiy, the spark gap unit includes an external annular electrode and an internal electrode supported concentrieally in substantially the same plane as the external electrode. The internal electrode is provided with an annular recess for aecommodating a permanent magnet which is, therefore, concentric with both the inner and outer electrodes. The permanent magnet produces a magnetic field between the electrodes by establishing flux lines oriented perpendieularly to the coplanar electrodes, while the are developed between the electrodes likewise establishes an electromagnetic field having flux lines encireling the are. The eleetromagnetic field of the are eoacts with the magnetic field of the are to spin the are away from the points of initial sparkover on the electrodes in a direction extending around the inner electrode. The are eontinues to move in a cireular fashion between the electrodes until the are eeases, thereby preventing severe distortion of the electrode surfaees at any point.

Other objects and advantages of the present nvention will become apparent from the ensuing description of an illustrative embodiment thereof, in the course of which reference is had to the aceornpanying drawing, wherein:

Fig. 1 is a seetional view of an aireraft lightning arrester embodying the new and improved spark :gap unit of the present nvention;

Fig. 2 is a seetional view taken along line 2-2 of Fig. l, assuming, of course, that the latter shows the entire structure, and illustrating in detail the construction of the spark gap unit;

Fig. 3 is a perspective view of the spark gap arrangement illustrating the location of the magnetic field; and

Fig. 4 is a schematie diagram showing an electrical circuit including the lightning arrester illustrated in Fig. l.

Referring now to the drawing and particularly to Fig. 1, there is illustrated an aireraft lightning arrester 10 which includes a spark gap unit 11 embodying the features of the present nvention. The aireraft lightning arrester 10 is identical to the arrester deseribed and elaimed in the above-identified Edward H. Yonkers et al. application with the exception of the spark gap unit 11. The arrester 10 is illustrated in an upright position suitable for mounting upon the fuselage 12 of an aireraft and is inserted through an aperture 13 defined in the fuselage. Specifically, a mounting plate 14 located intermediate the ends of the arrester 10 is secured to the fuselage by a plurality of spaced fasteners 15, for example, rivets. The plate 14 is of ring-like construction and is seeured to an outer hermetically sealed housing or envelope 16 and to an internal gasket sealed housing 18 disposed internally of and spaced from the housing 16. The housings 16 and 18 partially enclose and protect an internal assembly unit 2,9oe,922 W 24 including a surge blocking condenser 25. The housi ings 16 and 18 are connected to and support a pair of spaced apart connectors 20 and 22 respectively connected externally to an antennar26 and electric communication equipment 28 and respectively internally connected to the ends ,of the assembly unit 24. As indicated schematically in Fig. 4, the arrester Vincludes the spark gap unit 11, described in more detail hereinafter, for diverting high current surges intercepted by the antenna 26 to the fuselage 12 of the aircraft. One electrode 42 of the spark gap unit 11 is connected to the antenna 26 while the other electrode 40 is connected to the fuselage 12. Thus, the unit 11 shunts a series Vcircurit consisting of communication equipment`28v and assembly unit .24, the condens'er 25 of which couples the input signals from the antenna 26 to the equipment 28. To provide the described coupling, the connector is electrically connected to one of the condenser plates a comprising the external cover of the unit 24 while the connector 22 is electrically connected to the other condenser plate 2517. The unit 24 further includes a resistor connected between the plates 25a and 25b of the condenser 25 in order to provide a leakage path through the equipment 28 to ground 12 for any static charges built up on the antenna 26. The assembly unit 24 and its condenser 25 are constructed as described in detail in the Yonkers et al. application to which reference may be taken for a better understanding.

The spark gap unit 11, which is shown in Fig. 3, comprises an outer electrode 40 mounted upon the inner rim 14h of the mounting plate 14 and an inner electrode 42 mounted directly on the external cover 25a of the assembly unit 24. The outer electrode 40 is made from a material having good electrical conducting properties and is preferably machined from brass. As clearly shown in Figs. 1, 2 and 3, the electrode 40 is generally annular in configuration and includes an inwardly facing, cylindrical surface 40a interconnecting sides 40b having uniform widths. A groove 43 is cut in the outwardly facing surface of the electrode 40 and extends entirely around the electrode to define a pair of outwardly extending projections 46 and 48. The inner rim 14h of the mounting plate 14 is received within the groove 43, the width of 'the groove 43 and the thickness of the inner rim 14h being such 'that the electrode 40 and plate 14 are snugly mated together. The electrode 40 is fiXedly secured to the plate 14 by a plurality of fasteners, such as rivets 50, driven through aligned, spaced apart openings 52 provided in each of the outwardly extending projections 46 V and 48 and through aligned opening 54 defined in the inner rim portion 14b of 'the mounting plate. As indicated above, the inner rim portion 1417 of the mounting plate 14 is concentric with but spaced from the elongated assembly unit 24 so that the outer electrode 40 and particularly the inwardly facing surface 40a is concentric with the outer cylindrical surface of the assembly unit 24.

The inner electrode 42, like the outer electrode 40, is preferably made of brass and has a generally annular configuration. It includes an outwardly facing cylindrical surface 42a and a pair of sides 42b of uniform width. The electrode 42 has a central opening 420 so that it can be mounted upon the outer cover or plate 25a of the assembly unit 24. As shown, the cover 25a includes a first cylindrical portion 24a and a second cylindrical portion 24b of smaller diameter than the portion 24a, the cylindrical portions 24a and 241) being interconnected by a frustro-conical portion 24a. The inner electrode 42 is supported on the smaller'diameter cylindrical portion 24h and is restrained from movement longitudinally of the Vassembly unit 24 by a pair of sleeves 56 and 58. The

sleeve 56 has a tapered section 56a which is shaped to complement the frustro-conical portion 24c of the cover 25a and a cylindrical section 56b for engaging the portion 24b of the cover 25a. In order to position the sleeve on the unit 24, it is inserted over the antenna end of the assembly unit 24 and is slid along the smaller diameter portion 24h of the cover 25a until the tapered section 56a abuts against the frustro-conical portion 24a. Hence, the sleeve 56 provides a rigid abutment for one side 42h of the internal electrode 42. The other sleeve 58 is cylindrical and is shaped and dimensioned to engage the smaller diameter cylindrical portion 2417 of the cover 251'1.

In assembling the electrode on Vthe cover 25a, the sleeve 58 is inserted over the antenna end of the assembly unit 24 and is mov'ed along the smaller diameter vportion 2417 until the electrode 42 is tightly seated between the sleeves 56 and 58. The sleeve 58 may be secured position by deforming spaced regions of its thin wall into-f certain of the apertures 27 in the cover 25a of the unit,Z as by the use of a round end tool. ;i

lIt will be understood that the sleeve 56 is of such length. that the electrode 42 is aligned with the outer electrode 40 or, expressed in another way, is coplanar with the outer electrode 40. Moreover, the annular electrode 42 is concentric with the assembly unit 24 and with the outer electrode 40. The outer diameter of the electrode 42 is smaller than the inner diameter of the electrode 40 and, as a result, the inner face 40a of the outer electrode 40 and the outer face 42a of the inner electrode 42 are at all points equally spaced.

In accordance with a feature of the present invention, magnetic means are located within the inner electrode 42 to create a magnetic field between the electrodes 40 and 42 for the purpose of causing an arc developed between these electrodes 40 and 42 to move away from the points of initial sparkover on the electrode surfaces. More specifically, this magnetic means comprises an annular permanent magnet 44 which is seated within an annular recess 62 defined in the upper side 42h of the electrode 42 as viewed in Figs. 1 and 3; The recess 62 extends alrnost the width of the electrode 42 and is located adjacent the surface 42a between a thin wall 64 and the body of the electrode 42. The permanent magnet 44 is fixedly held within the'electrode 42 by peening the ends of the thin wall 64 over the magnet 44, as is best shown inFig. 1.

As best shown in Fig. 3, the axially polarized annular magnet 44 has one of its poles facing the connector 20 and its opposite pole facing the connector 22, which poles provide a plurality of fiux lines extending in the direction indicated by the arrowed lines 64. The fiux lines are oriented substantially perpendicularly to the plane of the concentric electrodes 40 and 42 and'in passing through the air gap are substantially parallel to the electrode surfaces 40a and 42a and to the longitudinal axis of the assembly unit 24. The flux lines pass through the entire space or gap between the electrodes 40 and 42.

Assuming that the antenna 26 Vintercepts a lightning surge having a voltage greater than the sparkover voltage of the spark gap unit 11, an arc is developed between the electrodes 40 and 42,.the current florw being from the e1ectrode42 to the electrode 40 as indicated by arrow pointed line 66 in Figs. 2 and 3. Immedately upon initiation of the arc, the arc moves away fromrthe initial sparkover points on the electrodes becauseof the interaction of the magnetic field of the arcV current with the field of the permanent magnet. Specifically, the coaction of the two fields produces a, force which acts on the arc to move it in the direction indicated by arrow pointed line 68, i.e., a clockwise direction aboutthe electrode 42 as viewed in Fig. 3; Of course, if the annular magnet 44 were turned upside down, then the flux Would be in an opposite direction andrtheV arc Would move radially ina counterclockwise direction about the electrode 42. In either case, the speed of circular movement of the arc increases with increasing amplitude of the sunge current, with the result that even though a greater surge current is flowing, the arc moves over the surfaces 40a and 42a at a faster rate and remains in contact with each element of the electrode surface for a shorter period of time.

In view of the foregoing description, it Will be recognized that severe pitting and scarring of the surfaces 40a and 42a of the electrodes is substantially eliminated since the arc moves continnously between radially aligned points on the electrodes. Moveover, since the gap distance between the electrodes 40 and 42 is um'form throughout, the arc is initially established between random radially aligned points on the electrodes. Accordingly, an arc is not repeatedly initiated between the same two points upon the occurrence of a series of lightning surges and the arc does not persist between the same points for an extended period of time, thereby avoiding pitting and scarring of the electrode surfaces.

While the present invention has been described in connection with the details of a particular embodirnent thereof, it should be understood that these details are not intended to be limitative of the invention since many modifications will be readily apparent to those skilled in this art and it is, therefore, contemplated in the accompanying claims to cover any such modifications as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by United States Letters Patent is:

1. In a lightning arrester, a spark gap arrangement comprising an outer annular electrode, an inner electrode concentric with said outer annular electrode, and magnetic means supported by one of said electrodes for producing a magnetic field between said electrodes to cause an arc developed between the electrodes to move 'around the inner electrode.

2. In a Lightning arrester, a spark gap arrangement comprising an outer annular electrode, an inner electrode concentric with said outer annular electrode, and magnetic means supported by said inner electrode for producing a magnetic field between said electrodes to cause an arc developed between the electrodes to move around the inner electrode.

3. In a lightning arrester, a spark gap arrangement comprising an outer electrode having a cylindrical inner surface, an inner electrode having an outer cylindrical surface, means for supporting said electrodes such that said surfaces of said electrodes are eqaidistant, coaxial and coplanar, and magnetic means supported by said inner electrode to develop a magnetic field between said surfaces substantially parallel to their axis, said field causing an arc developed radially in the gap between said surfaces to move between said surfaces.

4. In a lightm'ng arrester, a spark gap arrangement comprising an outer annular electrode, an inner electrode concentric with said outer electrode, and an annular permanent magnet supported internally of said inner electrode and concentric with said outer and inner electrodes, said magnet producing between said electrodes a magnetic field having flux lines parallel to the axis of said electrodes for moving an arc extendng radially between said electrodes around said inner electrode in a plane perpendicular to said axis.

5. In a lightning arrester, a spark gap arrangement comprising an outer annular electrode, an inner electrode concentric with said outer electrode and including an annular recess concentric with said electrodes, means for supporting said electrodes in coplanar relation, annular magnetic means located within said recess for providing between said electrodes a magnetic field having flux lines parallel to the axis of the inner electrode, said field cooperating with the current of an arc developed radially between the electrodes to move the arc around the inner electrode.

6. The spark gap arrangement of claim 4 wherein said recess is defined between a center portion and an annular wall of said inner electrodes and wherein one end of the wall is peened over the magnetic means to retain the magnetic means in the recess of the inner electrode.

7. In a lightning arrester, a spark 'gap arrangement comprising an annular outer electrode, an inner electrode concentric with said outer electrode and having first and second opposed sides, said electrode having an annular recess concentric with said outer electrode, and an annular permanent magnet located within said recess and having an annular north pole adjacent said first electrode side and an annular south pole adjacent said second electrode side, means for supporting said electrodes in generally coplanar relation, said magnet providing a magnetic field having fluX lines between said electrodes to cause an arc developed between the electrodes to move around the inner electrode.

8. A lightning arrester of the combined spark gap condenser type for use on aircraft to protect communication equipment from lightnin'g surges intercepted by an aircraft antenna comprising an insulated housing, a pair of connectors disposed at spaced positions on said housing, an assembly unit supported between said connectors and including a capacitor, an inner annular electrode supported from said unit and connected to said condenser, an external annular electrode supported from said housing and generally coplanar with said inner electrode, magnetic means supported within one of said electrodes and concentric with said electrodes, said magnetic means developing between said electrodes a field having fluX lines parallel to the axis of said electrodes for moving an arc developed between said electrodes around said inner electrode.

Hansell Jan. 28, 1936 Penning Dec. 5, 1939 

